1. Field of the Invention
The present invention relates to a high frequency circuit device such as a waveguide, a resonator, or the like including two parallel plane conductors, and a communication device using the high frequency circuit device.
2. Description of the Related Art
As transmission lines for use in a microwave or millimeter-wave band, different types of transmission lines are employed, such as grounded coplanar transmission lines each containing a dielectric plate having a ground electrode formed substantially on the whole of one face thereof and a coplanar line formed on the other face thereof, grounded slot transmission lines each containing a dielectric plate having a grounded electrode formed on one face thereof and a slot formed on the other face thereof, planar dielectric transmission lines each containing a dielectric plate having slots formed on both of the faces of the dielectric plate, in opposition to each other through the dielectric plate, and so forth.
All of these transmission lines are formed so as to contain two parallel plane conductors. Therefore, there has arisen the problem that if an electromagnetic field is disturbed in input-output portions and bends of the transmission lines, a spurious mode wave such as a so-called parallel plate mode wave or the like is excited between the two parallel plane conductors, and the spurious mode wave is propagated between the plane conductors. In some cases, problematically, interference is caused by the spurious mode leakage wave between the adjacent transmission lines, so that a signal leaks between the lines, and so forth.
FIG. 62 shows an example of the principal propagation mode of a grounded coplanar transmission line and a parallel mode electromagnetic field distribution generated incidentally to the principal propagation mode. In FIG. 62, an electrode 21 is formed substantially on the whole of the lower face of a dielectric plate 20, and a strip conductor 19 and an electrode 22 are formed on the upper face thereof. The electrodes 21 and 22 are used as ground electrodes. These electrodes, the dielectric plate 20, and the strip conductor 19 constitute a grounded coplanar transmission line. In such a grounded coplanar transmission line, an electromagnetic field is disturbed at the end portions thereof, so that an electric field is induced, extending vertically to the electrodes 21 and 22 on the upper and lower faces of the dielectric plate 20, and thereby, a parallel plate mode electromagnetic field is generated as illustrated in FIG. 62. In FIG. 62, solid line arrows, broken lines, and alternate long and two dash lines represent an electric field, a magnetic field, and a current distribution, respectively.
Conventionally, for the purpose of preventing propagation of such an undesired mode wave, through-holes electrically connecting electrodes formed on the upper and lower faces of a dielectric plate, are provided along a transmission line, on both of the sides thereof and at intervals sufficiently short with respect to the propagation mode wavelength. When these through-holes are provided along the propagation direction of a waveguide electrically connecting the electrodes on the upper and lower faces as described above, the through-hole parts act as electrical walls, where propagation of the parallel plate mode wave is prevented. However, in a high frequency range such as a millimeter wave band or the like, it is required to reduce the thickness of the dielectric plate so that generation of higher mode waves can be suppressed. Moreover, it is necessary to greatly reduce the intervals between the through-holes. Accordingly, a high precision production process is required.
In the case in which no through-holes are provided in the dielectric plate, it is conceivable to employ a method of mounting the entire dielectric plate having electrodes formed thereon into a cutoff waveguide. However, the size of the cutoff waveguide must be reduced to be less than half of the guide wavelength. Restrictions on the size of the transmission line become severe.
Moreover, it is also conceivable to employ a method of blocking the propagation of a spurious mode wave in which an electrode is partially removed in the area where the spurious mode wave leaks, so that a magnetic wall is formed. However, in this case, the new problem arises that the area where the electrode is removed acts as a kind of resonator.
The applicant of the present invention has filed Japanese Patent Application No. 11-025873 on a spurious mode wave propagation blocking circuit in which inductors and capacitors are combined to form a lumped-constant circuit and are arranged in a two dimensional form.
The present invention provides a high frequency circuit device and a communication device which can solve the problems, caused by propagation of a spurious mode wave, similarly to the above Japanese Patent Application No. 11-025873, and in which the pattern can be more reduced in size as compared with the circuit described in Japanese Patent Application No. 11-025873.
To accomplish these results, according to one aspect of the present invention, there is provided a high frequency circuit device which comprises at least two parallel plane conductors, a circuit for exciting an electromagnetic wave, provided between the two plane conductors, and a spurious mode wave propagation-blocking circuit for coupling to a spurious mode wave propagating between the two plane conductors to block the propagation of the spurious mode wave, formed on either or both of the two plane conductors, the spurious mode wave propagation-blocking circuit comprising a plurality of arranged fundamental patterns each made of a strip conductor and constituting a multi-port circuit having at least two ports, the strip conductor of the two-port circuit being determined so that any arbitrary two-port circuit of the respective fundamental patterns has a band-stop filter characteristic.
For example, as shown in FIG. 1, between ports #1 and #4 of a four-port circuit, a circuit is provided which functions as a band-stop filter BEF between the ports #1 and #4, as well as between each adjacent pair of the other ports. That is, band-stop filter circuits are presented between ports #1 and #2, between ports #2 and #3, and between ports #3 and #4, respectively. In FIG. 1, the ground terminals corresponding to the ports #2 and #3 are not shown.
As regards the total reflection condition of a multi-port circuit, as described below, if a circuit between two arbitrary ports satisfies the total reflection condition, irrespective of the symmetry of the circuit, the total reflection condition of the whole of the circuit is satisfied. Thus, by arranging plural polygonal fundamental patterns each constituting such a multi-port circuit as shown in FIG. 1, a spurious mode wave such as a parallel plate mode wave propagating between two plane conductors couples with the patterns, so that propagation of a spurious mode wave can be prevented.
According to a further aspect of the invention, a strip transmission line with an open end, having an electrical length equal to xc2xc wavelength at a service frequency is connected in parallel to a strip conductor of the two-port circuit, e.g., as shown in FIG. 2. Thereby, an arbitrary two-port circuit can present a band-stop filter characteristic.
According to a further aspect of the invention, the two-port circuit comprises at least two strip conductors having an electrical length difference equal to a half wavelength and connected in parallel to each other between the two ports of the two-port circuit, e.g., as shown in FIG. 3. In this case, a band-stop filter is configured only by the strip conductors provided between the two arbitrary ports.
According to a further aspect of the invention, a transmission line having a predetermined impedance and a predetermined electrical length is connected to each of the input-output ports of the fundamental pattern. Thereby, the frequency band having the above-described band-stop characteristic can be increased in width. Thus, propagation of a spurious mode wave can be blocked over a wide band.
In a communication device according to an aspect of the present invention, the above-described high frequency circuit device is used as a communication signal propagation section or a communication signal processing section, in combination with transmitting and/or receiving circuits.